Interannual variation of tropical cyclone energy metrics over North Indian Ocean

There is decreasing trend in the tropical cyclone (TC) number over the North Indian Ocean (NIO) in recent years, though there is increasing trend in the sea surface temperature (SST) which is one of the main environmental parameters for the development and intensification of TCs. Hence, a study has been performed to understand whether any trend exists in other TC parameters such as velocity flux (VF), accumulated cyclone energy (ACE) and power dissipation index (PDI). The interseasonal and interannual variations of VF, ACE and PDI for the NIO as a whole and Bay of Bengal (BOB) and Arabian Sea (AS) are analysed based on the data of 1990-2013 (24 years). Role of large scale features like El Nino southern oscillation (ENSO) and Indian Ocean dipole (IOD) have also been analyzed. The mean ACE per year for TCs [maximum sustained wind of 34 knots (kt) or more] over the NIO is about 13.1 x 10(4) kt(2) including 9.5 x 10(4) kt(2) over the BOB and 3.6 x 10(4) kt(2) over the AS. The mean PDI per year for TCs over the NIO is about 10 x 10(6) kt(3) including 3 x 10(6) kt(3) over the AS and 7 x 10(6) kt(3) over the BOB. The VF, ACE and PDI of TCs are significantly less over BOB during post-monsoon season (Oct.-Dec.) of El Nino years than in La Nina and normal years. The VF for TCs over the BOB during post-monsoon season is significantly less (higher) during positive (negative) IOD years. There is significant decreasing trend at 95 % level of confidence in ACE and PDI of TCs over AS during post-monsoon season and PDI over the BOB and NIO during pre-monsoon season mainly due to similar trend in average intensity of TCs and not due to trends in SST over Nino regions or IOD index.